Sartorius Stedim Biotech MD8 airscan, Operating Instructions Manual, Page: 42 / 57

9.5 Dissolving the gelatin filter prior to evaluation of collected microorganisms
Gelatin filters can be dissolved in 100 ml of sterile liquid, such as physiological saline
or 0.1% peptone water, warmed to 40°C. Dissolution should be finished within about
15 minutes. Stirring the liquid using a sterile magnetic stirrer accelerates dissolution
of the filter.
The solution can then be processed by a pour plate or membrane filter method.
During the dissolving and stirring process, groups of microorganisms are separated into
individual microorganisms, so that a higher count will be obtained with this method than
by direct plating of the gelatin filter. This method is recommended when very high colony
counts are expected (dilution series) or when sampling is carried out in areas which have
been sprayed with disinfectants or where antibiotic dust could be present (subsequent
filtration of the solution through an 0.45 μm cellulose nitrate membrane filter, e.g. 11406,
and rinsing this with an osmotically appropriate sterile medium prior to incubation, ensures
removal of growth inhibiting substances).
9.6 Dissolving the gelatin filter after collecting viruses and phages
When the virus concentration is to be determined, a gelatin filter must be used and
subsequently dissolved, so that retained viruses (phages) can be cultivated in the solution
and analysed by virological or molecular biological methods. Detailed procedural information
is given in the application notes “Collecting Airborne Viruses and Phages Using the Gelatin
Membrane Filter Method” and “A method for detecting and enumerating airborne virulent
bacteriophage of dairy starter cultures” (publication numbers SLF-4028-e and SM-4021e
respectively) as well as in further publications on this topic.
Further information on request.
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